Tire underinflation has always been a serious concern to the trucking people as well as the Federal and State Highway people. An underinflated tire, usually caused by a slow leak resulting from a malfunctioning air valve, causes shorter tire life, more fuel expenditure and increased wear on the highway surface. All parties involved in use and care of the highway system would benefit from a practical solution that yields a timely warning of underinflated tires for the following reasons:
A. Truck fleets would save on fuel, tires, labor and road "downtime".
B. Federal and State highway authorities agree that proper and practical tire pressure control would assist in the maintenance of road surface condition, extend the life of the road systems and decrease road repair expenses. The reason is that a slow leak in one tire of a dual tire arrangement increases the dynamic impact characteristics on the road. The greater the transfer of load from "leaker" to the good tire the greater the potential damage to good tire and road surface. The current weigh stations enforce the law with respect to axle loading and rating of tires for specific axle loading; however, there is no provision for checking the working tires as a support system with respect to said axle loading. Information with respect to the effective tire foot print area supporting a given load is most important, since it defines unit pressure exerted on the road service by the support members. It is our belief that this passive system will complement the present weigh station system. The need has existed for years for a passive system which would INDICATE underinflated tires on a moving rig without any DIRECT human contact with the vehicle. This passive system alerts the driver of a pending or existing underinflation problem. The setting of alarm levels of pressure loss should be decided between highway management and trucking management since these parameters must reflect the necessary trade-offs of the actual practical field operation.
C. The public would appreciate the higher quality of road surface and the cost savings on road construction and repair.
There have been a number of designs to detect the underinflation tire problems in heavy "over the road" vehicles. To this point none have sold successfully because of a combination of high initial cost, increased operational and maintenance costs and unsatisfactory field experiences. The reason for the high costs is that all prior systems have directed their attention to mounting the sensor devices on each individual tire of the vehicle. It is time to revisit the low pressure tire problem with a new evaluation of how to solve the problem. It is necessary to accept certain basic facts as follows:
1. It must be recognized that successful commercial fleets are well maintained and that few trucks leave the company garage area with low tires, brake drag or bad bearings.
2. It must be recognized that modern drivers are better trained and are working with much better equipment than in the past. Todays drivers are equivalent to mid-level managers in a manufacturing corporation and handle their work with a great degree of competence.
3. It must be recognized that the manufacturers have made great strides in the design of modern tires, brakes and axle bearings. The incidence of catastrophic tire/wheel failures are quite rare.
4. It must be recognized that over ninety five per cent of the problems of a tire/wheel assembly result from the slow tire leaks usually caused by unseating and damage to the tire valve. Unfortunately, the best maintenance department cannot protect the rig from the results of such slow tire leaks while long haul vehicles are miles away from the maintenance base for prolonged periods of time. In a profitable trucking operation, the time a big rig is away from home maintenance center is at least 85% to 90% of rig life. It is during this dynamic road time that symptoms of a tire pressure problem are the most apparent and can be corrected before additional vehicle operational costs and damage to road surface are incurred. This system will also reduce needless tire pressure checking with the air pressure gauge which is very often the cause of the slow leaking tire/wheel assembly.